Irwin is a borough in Westmoreland County, Pennsylvania, United States.

[4] Irwin was the original western terminus of the Pennsylvania Turnpike when it opened in October 1940.

[5] Brush Hill was listed on the National Register of Historic Places in 1975.

[6] According to the United States Census Bureau, the borough has a total area of 0.9 square miles (2.3 km2), all land.

39.5% of all households were made up of individuals, and 15.1% had someone living alone who was 65 years of age or older.